Method
In a small, shallow bowl, sprinkle the yeast and 1/2 teaspoon of sugar over 1/2 cup of lukewarm milk. Let the mixture stand for 2 or 3 minutes, then stir to dissolve the yeast completely. Set the bowl aside in a warm, draft-free place, such as an unlighted oven, for 5 to 8 minutes, or until the mixture doubled in volume.
In a deep mixing bowl, combine the remaining sugar with salt and flour. Make a well in the center and pour in the yeast mixture. Add the remaining milk, drop in the eggs and, with a large spoon stir the flour into the liquid ingredients. Continue to stir until fairly stiff dough is formed. Knead the dough by pulling it with your hands---as you might be pulling taffy---for about 10 minutes, or until it is smooth and elastic. Drape the bowl loosely with a kitchen towel and set it aside in the warm, draft-free place for 1 hour, or until the dough doubles in bulk. Then punch it down and knead in 3/4 pound of the softened butter, a tablespoon or so at a time. Knead in the currants and sultana raisins.
With a pastry brush, coat the inside of a 12-cup mold with the remaining 2 tablespoons of softened butter. Pat the dough into the mold; it should come about halfway up the sides. Cover the mold loosely with a kitchen towel and set aside in a warm, draft-free place for about 1 hour, or until the dough has doubled in volume and has risen almost to the top of the pan. Preheat the oven to 400° F.
Bake the cake in the center of the oven for 10 minutes, then lower the heat to 350° and bake another 35 minutes. Remove from the oven, drape a kitchen towel loosely over the top of the mold and let it rest for 5 minutes. Run a knife around the inside of the mold and turn the cake out into a serving dish. Then carefully turn the cake over on the plate.